Ethernet devices conforming to the Institute of Electrical and Electronics Engineers (“IEEE”) 802.3 standard (March, 2002) perform a configuration sequence to transmit at a highest common transmission speed between the devices and one of two transmission modes, half duplex or full duplex. In full duplex mode, data can be transmitted and received simultaneously and in half duplex mode data can only be transmitted or received separately and not simultaneously. If the stations do not configure themselves at a same duplex level, then collisions may occur and fragmented packets having (cycle redundancy code) CRC errors are received, which results in a substantial degradation of performance and transmission errors.
During configuration, devices capable of auto negotiation may advertise their transmission capabilities to allow the devices to take maximum advantage of their abilities. If both stations engage in auto negotiation, then they establish a link at the highest common speed and duplex capability. If auto negotiation is only enabled in one of the stations, then the station with auto negotiation will use parallel detection to determine the speed of the link partner and communicate at the highest common speed and set the duplex mode to half duplex. If the stations transmit at a common speed, then a link is established. However, when the station with auto negotiation transmits in its default half duplex mode, transmission errors and degradation occur if the link partner transmits at full duplex.
In certain situations, an Ethernet adapter may be programmed to transmit at a forced speed and duplex mode. In such case, if both adapters are forced to the same speed and different duplex modes, then a link is established, but substantial degradation and errors occur due to the different duplex modes. If the forced speeds are not the same, then links will not be established. If the linked stations are forced to the same speed and duplex mode, then transmissions will occur without significant errors.